Damsels will usually bully each other to the death. You will probably end up with one fish at the end. At the pet store, they aren't in the tank long enough to establish a territory. And the ones that do get killed are removed from the tank, so you don't see it happening. In your home aquarium, the aggression will escalate over time. Damsels will kill other fish too. In my experience, the worst offenders are blue damsels, domino damsels and striped damsels. I would avoid those fish if you want to keep anything but the damsel. And you will be maxed out at 3 fish in your tank anyways.